Improvement in calipers



UNITED STATES Y PATENT OFFICE.

ROBERT D.. O. SMITH, OF WASHINGTON, DISTRICT OF COLUMBIA.

IMPROVEMENT IN -CALIPERS Specification forming part of Letters PatentNo. 45,5 29, dated'DccemberY 20, 1864. I

l'o aZZ whom it may concern.-

Be it known that I, ROBERT D. O. SMITH, of the city ot Washington andDistrict ot' Columbia, have invented a new and Improved Mode ofConstructing Calipers ;y and I-hereby declare the following to beafnlLclear, and exact description ofthe same, reference beinghad to theaccompanying drawings, in which- Figures 1, 2, and 3 exhibit my improvedcalipers in various positions; and Figs. Ltand 5 exhibit another form'of theinstrument providedwith supplemental points. Y

The nature of my invention consists in providing calipers having only asingle pair ot legs with a double scale, so that the sameinstrument-canbe used either for inside or outside measurements, and the diameterdetermined immediately without the aid of any othetlnstrument. f

I construct my instrument with legs of the ordinary shape, but with theupper end, or that pait beyond the joint, tiattened and eX tended into abroad plate, as shown in Fig. 1,.

the end or outer edge describing 'the arc of a circle whose center isthe center otl the pivot upon which the legs move, and' the two sideedges forming an angle to eachother ot' about ninety degrees. One ofthese plates is shorter than the other, and its outer edge thereforeVforms an arc ot' a smaller circle. This edge may be chamfered thin forthe purpose of V more conveniently having a scale marked upon it. Thecenter line, o, cutting both plates, is the Zero-point, and measurementsfor outside work run one wayV from this point, while the measurementsfor inside run the other way,

f as will he understood without-diculty by pointsof the legs touch eachother, as in Fig.

l. If now the points ot' the legs be moved asunder-sayone-quarterinch-the zero-point otl the/smaller or inner scale moves overthe larger arc a distance indicated .by the to the smaller arc, as shownin Fig. 3, in which` the distance indicated is two inches. VIn short,

the distance indicated in regularorder bef tween the zero point of thelarge scale and the zero-point o f the small one isthe distance whichseparates the points of the legs.

If desired, the two scales may be separatedentirely, one being putuponjthe larger arc, and the other being put uponthe smaller one,

4as shown in Fig. 6. The zero-points are then placedupon the end ofeaiohscale. respectivel Though this plan` mayT appear most simple, I

think itmore likely to lead to mistakes' than the method illustrated byFigs. 1, 2, and 3.

The advantages to be gained by my im-' provements consist, first, in thefacility with which diameters, either internal or external,-

may be measured without the aid ot' a rule or detached scale; and,secondly, in the power of the instrument to determine diameters whichotherwise would be inaccessible, as in Figs. 2 and 4, theinstrument inFig. 2v being represented in the act o f measuring the -int-eriordiameter'of a cavity whose mouth or oritice is much smaller than .the.point to be measured, and FigA. representing lthe instrument asstraddling over a projecting edge to measure a diameter behind it, thediameter in either case being read while the points are resting upon thesurface whose distance asundcr it is desired to messure. 1

4I am'aware that .calipers have been made with a single' scale and apointer, so Vthat an instrument might be made to measure either outsideor .inside diameters andindieate the It desired, supplemental points maybe addsame by means of the said scale; but I am'not aware that-anyinstrument has been made combining both Ythese capabilities in oneiustrument.

In speaking of'eelipers, I desire to be understood-'as referring onl5Tto calipers of the common ,form with bent legs, as represented, andturning upon a pivot.-

Having described my invention, .what I Gleim as new, and desire tosecure by Letters Patent, is- Y 1. Calipers having only one pair of legsand provided with two scales, so that the same 4palriof legs may be usedfor either inside or outside' measurements, and the diameters measuredbe determined by said scales with out the aid of rule or detached scale,substantially as described. r

2. A double scale for calipers with a single pair of legs when one-halfof each seele is upon one blade, and the other halt of each scale isupon the other blade, of the calipers, substantielly as described.

R. D. O; SMITH.

Witnesses:

ANDREW WHITELEY, W. O. DODGE.

